Medical balloon catheters are tube-like medical instruments that are inserted into a body cavity, tract or duct or blood vessel for location of a deflated balloon at a vascular site and remote inflation at the site for diagnostic or therapeutic reasons. Balloon angioplasty catheters are widely used in angioplasty procedures for efficiently and effectively opening stenoses in the coronary arteries and in other parts of the vascular system. The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Using fluoroscopy, the physician guides the catheter through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying a fluid under pressure through an inflation lumen to the balloon. The inflation of the balloon causes stretching of the artery and pressing of the lesion into the artery wall to re-establish acceptable blood flow through the artery.
One important characteristic of a dilatation catheter used for angioplasty is its profile, i.e., the outer diameter of the distal end portion of the balloon. Considerable effort has been spent in developing low-profile dilatation balloon catheters by minimizing the dimensions of the core or inner tube which extends through the balloon to its distal end, and by reducing wall thickness, to the extent possible, of the balloon itself.
Another important consideration is the outer diameter of the catheter in its deflated condition. This outer diameter affects the ease and ability of the dilatation catheter to pass through an introducer or guide catheter and through the coronary arteries leading to the stenosis to be opened.
The angioplasty balloon material, thickness, and length are selected to provide an inelastic balloon capable of being inflated to a predetermined diameter and length and to exert relatively high pressure against an occlusion of a blood vessel wall to expand it or to fracture it. Because the balloon material is not elastic, it has a fixed inflated diameter and it cannot deflate to a smaller diameter than its inflated diameter. Thus in the deflated state, the balloon material collapses upon itself forming flaps or wings that must be folded or wrapped around the balloon catheter to allow it to be withdrawn from the patient's vascular system after it is used. And, before it is used, the balloon catheter has to be folded or wrapped about the balloon catheter body to fit within and pass through the guide catheter lumen. When inflation fluid is applied to the deflated balloon, it causes the balloon flaps to unwrap so that the balloon can inflate to its fully inflated condition. Such balloon catheters are disclosed, for example, in commonly assigned U.S. Pat. Nos. 5,690,613 to Verbeek and 5,350,361 to Tsukashima et al., both incorporated herein by reference.
Various techniques or balloon constructions are employed order to encourage the balloon to fold about the balloon catheter body in a uniform manner when it is evacuated in two or three or four or more flaps or wings of the same size. One approach has been to construct the balloon of a cylinder of material, e.g., polyethylene, that is uniform about its circumference but can be heat set after it is wrapped or folded to form curved, overlapping flaps or wings extending from fold lines in a manner described further below. Another approach has been taken to fabricate the balloon itself with fold line structures and flap shapes, particularly for use with balloons formed of stronger polyesters e.g. polyethylene terepthalate (PET). These techniques are set forth, for example in U.S. Pat. Nos. 5,053,007, 5,147,302 and 5,342,307 to Euteneuer, U.S. Pat. No. 5,087,246 to Smith, U.S. Pat. No. 5,147,302 to Euteneuer et al., U.S. Pat. Nos. 5,163,989, 5,456,666, and 5,458,572 to Campbell et al., U.S. Pat. No. 5,209,799 to Vigil, U.S. Pat. No. 5,226,887 to Farr et al., and U.S. Pat. No. 5,318,587 to Davey and in commonly assigned U.S. Pat. No. 5,350,361 to Tsukashima et al., all incorporated herein by reference. In the Euteneuer '107, '302 and '307 patents, "tri-fold" balloons are formed by folding the balloon along fold lines of the balloon located 120.degree. apart around the balloon circumference and then subjecting the folded balloon to an initial heat treatment to set the fold lines. In the Tsukashima '361 patent, the tri-fold balloons are folded in a similar manner and then the fold lines of the balloon located 120.degree. apart around the balloon circumference are subjected to heat treatment to set the fold lines. The remaining cited patents disclose other fold line structures for inelastic medical balloons including angioplasty balloons, intra-aortic balloons and esophageal dilatation balloons.
In the prior art, it has been common to use a balloon protector in conjunction with such balloon dilatation catheters. A balloon protector serves at least two important functions. First, it protects the balloon and distal tip of the catheter from possible damage during shipping and handling before it is removed. Second, the balloon protector keeps the balloon tightly wrapped in its deflated condition to minimize the outer diameter of the balloon in its deflated state.
A balloon protector is typically applied to the distal end portion of the catheter prior to sterilization of the catheter. The sterilization process can involve exposing the catheter, with the balloon protector in place, to an elevated temperature for a period of time. With certain balloon materials, e.g., polyethylene (PE), the sterilization process will advantageously cause the balloon to be heat set in the folded or wrapped configuration in which it is held by the balloon protector. As a result, when the balloon protector is later removed, the balloon remains in this tightly wrapped or folded configuration.
The heat setting of a balloon has the further advantage that when the balloon is inflated and then deflated, as it may be several times during an angioplasty procedure, the application of negative pressure during deflation will cause the balloon to return fairly closely to its tightly wrapped heat set configuration. This greatly facilitates the removal of the catheter after the procedure has been performed.
Various types and configurations of balloon protectors have been shown in the prior art, for example, in the above-incorporated Euteneuer '107, '302 and '307 patents and in commonly assigned U.S. Pat. Nos. 5,352,356 to Jung et al. and 5,425,710 to Khair et al., U.S. Pat. No. 4,901,707 to Schiff, U.S. Pat. Nos. 4,738,666 and 4,710,181 to Fuqua, U.S. Pat. No. 5,066,298 to Hess, U.S. Pat. No. 5,137,512 to Burns, and U.S. Pat. No. 4,540,404 to Wolvek, all incorporated herein by reference.
The above-incorporated Fuqua '666 and '181 patents propose a catheter protector comprising a hollow cylindrical sheath. The Fuqua sheath covers the entire length of the catheter, and is removed by pulling it off of the proximal end of the catheter. Fuqua also proposes providing perforations in the sheath for facilitating its removal. A similar arrangement is proposed in the above-incorporated Wolvek '404 patent, in which a sheath is slidably disposed over a substantial section of a catheter body, covering the balloon disposed at the distal end of the catheter body. The sheath and catheter assembly are advanced into the patient's vascular system until the distal balloon end is positioned in the area to be dilated. The sheath is long enough that its proximal end remains exposed outside of the patient, such that the sheath may be withdrawn along the catheter body until the balloon is uncovered. Then, the dilatation procedure can be performed.
The above-incorporated Euteneuer '007, '302 and '307 patents also disclose use of a compression protector employing an inner sleeve applied over a deflated balloon, an outer sleeve applied over the inner sleeve, and a compression housing for compressing the outer sleeve radially in on the inner sleeve, thus compressing the inner sleeve radially in on the balloon. With the balloon thus compressed within the Euteneuer protectors, the catheter is then sterilized at an elevated temperature. The inner and outer sleeves are formed of materials which exhibit heat-shrink qualities such that the heat treatment causes the balloon to be further compressed to a smaller outer diameter along the previously formed fold lines. The Euteneuer protectors are removed just prior to introduction of the catheter into the patient, with the balloon retaining its compressed form as a result of the heat treatment.
The above-incorporated Hess '298 patent proposes protecting a catheter's balloon by wrapping the balloon with tape in an overlapping fashion. In a manner similar to that proposed in the Euteneuer patents, the Hess '298 balloon is subjected to heat treatment after being wrapped, in order to further compress the balloon and affect a heat-setting of the balloon in its compressed condition.
In the above-incorporated Burns '512 patent, a multi-segment balloon protector is disclosed formed of two or more Teflon.RTM. PTFE tubes, usually axially aligned and of different diameters. Less force is required to apply the protectors, resulting in a lower chance of tearing the balloon when the protector is applied.
The above-incorporated, commonly assigned '236, and '710 patents disclose improved tubular sleeve balloon protectors that receive the folded or wrapped balloon within elongated sleeve lumens without requiring twisting of the balloon in order to advance it into the sleeve lumens. A split inner sleeve of lubricious material is employed in the '236 patent, and a coating of lubricious material, particularly parylene, on the sleeve lumen surface is disclosed in the '710 patent. The balloon protector shrinks during heat sterilization to tightly hold the balloon in the folded condition and heat set the folds of the balloon.
The use of a rigid balloon protector formed of two elongated half sections that are fitted over to enclose a folded intra-aortic balloon having an integral stylet formed therein and then attached together is disclosed in the above-incorporated Schiff '707 patent. The initial wrapping of the balloon about the integral stylet and catheter body extending through the balloon is apparently accomplished manually before the wrapped balloon is placed into the tubular opening of the elongated half sections.
While these techniques have aided in forming inelastic medical balloons that tend to refold or rewrap their flaps about fold lines, it is still necessary at times to rewrap the balloons after they have been removed from the balloon protectors and are outside of the patient's body.
The necessary tightness of the winding and reduction of the folded balloon diameter cannot be achieved readily by simply manually twisting the balloon folds around one another. Moreover, manual twisting of the balloon can damage it. In order to overcome this problem, it has been customary to provide a refolding or rewrapping tool kit with the balloon angioplasty catheters that the physician employs to tightly wind the balloon flaps around one another. These kits include the Sci-Med.RTM. Wrap-It.TM. refolding tool included with the Sci-Med.RTM. NC Bandit.TM. PTCA catheter, the CDV.TM. balloon refolding tool sold with the CVD FACT.TM. PTCA catheter by the assignee of the present invention, and the ACS.RTM. balloon sheath. The ACS.RTM. balloon sheath constitutes a simple protector tube having a flared, conical end opening that is used as a balloon protector as described above and which is stated to be used as a "regrooming" sheath. The WRAP-It.TM. refolding tool is a plastic tubular member having a tool lumen extending therethrough an a flared conical end and a relatively stiff, short mandrel or stylet having an eyehook at one end. In use, the stylet is inserted through the tool lumen so that the straight stylet end extends from the flared lumen end opening. The straight stylet end is inserted into the distal end opening of the PTCA catheter lumen, and the user then pinches and rolls the balloon between the fingers to advance it over the sylet and through the tool lumen to roll the balloon flaps into the spiral. Several passes may be required because the tool only comes in one tool lumen size for all balloon sizes. The CDV.TM. balloon refolding tool also comprises a tool and wire stylet of this type except that it is provided in different tool lumen sizes to receive different sized balloons and in that the stylet eye hook end is fixed in the tool lumen at the straight end.
The use of rewrapping or refolding tools for rewrapping flaps of inflexible intra-aortic balloons has also been disclosed in U.S. Pat. No. 4,444,186 to Wolvek et al. and in U.S. Pat. No. 4,681,092 to Cho. In the Wolvek '186 patent, a wrapping guide is disclosed that aids in spirally wrapping an intra-aortic balloon immediately before it is inserted into and through the guide catheter lumen. In the Cho '092 patent, a several part wrapping apparatus for wrapping a bi-fold, intra-aortic balloon is disclosed. Two half sections that fit together receive the deflated balloon and a shoe and biasing member in an elongated channel that has channel extensions that receive the two deflated flaps. After assembly, the catheter body is twisted to rotate the balloon and pull the flaps from the outlying channels and wrap them around one another and the catheter body. This twisting and pulling motion can cause damage to fragile balloon structures and is awkward.
Notwithstanding such proposals, however, there is perceived by the inventors to be a continuing need for improved balloon rewrapping or refolding tool and method for rewrapping balloon flaps of medical balloon catheters.